Polycarbonate is a thermoplastic that has excellent mechanical properties such as impact resistance, heat resistance and transparency. Polycarbonate is widely used in many engineering applications.
Polycarbonates may be prepared by several processes (U.S. Pat. No. 6,177,536) including: i) Interfacial, wherein a multiphase reaction process a dihydroxy aromatic compound is first reacted with phosgene in the presence of a small amount of monohydroxy aromatic compound and then precipitated and dried to yield a polycarbonate powder; ii) A melt process in which phosgene is reacted with a monohydroxy aromatic compound in the presence of an alkaline catalyst to yield a carbonic diester that is polymerized in a multistage reactor in the presence of a dihydroxy aromatic compound to yield a molten polycarbonate; iii) A melt process in which a non phosgene route is used to obtain a carbonic diester that is polymerized in a multistage reactor in the presence of a dihydroxy aromatic compound to yield a molten polycarbonate (U.S. Pat. No. 5,525,701); and iv) A melt process in which a phosgene route is used to obtain an ester substituted diaryl carbonate that is polymerized in a multistage reactor in the presence of a dihydroxy aromatic compound to yield a molten polycarbonate (U.S. Pat. No. 4,323,668).
U.S. Pat. No. 4,323,668 describes a reaction between BPA and BMSC to produce BPA homopolymer polymers. The patent states that use of (ortho-alkoxycarbonylaryl) carbonate substrates provides—when contrasted with bis(ortho-haloaryl)carbonates—the following advantages: (1) improved transesterification reaction rate, (2) less polycarbonate color formation during the transesterification reaction, (3) milder transesterification reaction conditions including lower temperatures, (4) reduced amounts of carbonate substrate since only stoichiometric amounts or amounts slightly in excess are required for complete conversion of all dihydric phenol to polycarbonate, and (5) reduced or equivalent quantities of catalyst at improved reaction rate, temperature and pressure transesterification reaction conditions.